"Mr. Tillerson, do you agree with President-elect Trump when he said, 'It wouldn't be a bad thing for us if Japan, South Korea or Saudi Arabia acquired nuclear weapons?'" Markey asked.

"Senator, I don't think anyone advocates for more nuclear weapons on the planet," Tillerson replied.

Markey pressed if Tillerson agreed with Trump that proliferation would not be a bad thing. "I do not agree," Tillerson said.

"Senator, I think if confirmed, it is a vital, one of the vital roles for the State Department to play ... has to be the pursuit of nuclear nonproliferation," Tillerson continued. "We just simply cannot back away from our commitment to see a reduction in the number of these weapons on the planet."

But Tillerson came to Trump's defense when asked about the president-elect's tweet saying the U.S. must "expand" its nuclear capability.

"I think in the context of some of the quotes that you're running through here, the president-elect has also indicated a commitment to ensuring that the level of nuclear arms and capability that we are going to maintain under agreed treaties, that those capabilities must be maintained," Tillerson said.

Trump has been all over the map when it comes to nuclear nonproliferation. In 2016, he seemed to say that Japan might be better off if it had nuclear weapons to defend itself from North Korea. At a town hall last April, he also seemed to support Saudi Arabia's having nuclear weapons but quickly reversed himself. And in June, he denied that he wanted Japan to get nuclear weapons.